The molecular sieve is a material widely used in the catalytic cracking catalyst, and is also an important component of the catalytic cracking catalyst. The property of the molecular sieve directly affects the reaction performance of the catalytic cracking catalyst. According to different demands, the molecular sieve can be modified in different ways so as to satisfy the use requirement. For example, a molecular sieve with a high silica-alumina ratio is generally considered as being required by the catalytic cracking catalyst.
In the preparation of a molecular sieve with a high silica-alumina ratio, there are the following processes: dealumination and silicon insertion with ammonium hexafluorosilicate, hydrothermal dealumination and silicon insertion, and gas-phase dealumination and silicon insertion (also called as gas-phase ultra-stabilization).
Dealumination and silicon insertion with ammonium hexafluorosilicate (also called as chemical dealumination and silicon insertion) can produce a molecular sieve with a high crystallinity, a high Si/Al ratio and a high thermal stability. The insoluble substance AlF3 and the residual fluorosilicate formed in the dealumination can affect the hydrothermal stability and also pollute the environment.
The hydrothermal process is now widely used in the industry. However, due to the late silicon insertion after dealumination, it is easy for the hydrothermal process to cause the collapsed crystal lattices, and the non-framework aluminum fragments block the pore channels, which not only affect the accessibility of the active centers, but also affect the further improvement of the thermal stability.
Gas-phase chemical dealumination and silicon insertion has the characteristics of uniform dealumination and timely silicon insertion. The resulting product has a high crystallinity retention and a good thermal stability; and the pore channels of the product are expedite.
CN1121903C discloses a process for preparing a rare-earth containing high silica Y-type zeolite, which process comprises: a rare-earth containing Y-type zeolite is dried to the water content of less than 10 wt %, a gas of tetrachlorosilane carried by a dried air is introduced at a weight ratio of tetrachlorosilane:Y-type zeolite=0.1-0.9:1, and the reaction is conducted at 150-600° C. for 10 minutes to 6 hours; after reaction, the purge with a dried air is conducted for 5 minutes to 2 hours; the resulting zeolite is washed with a decationized water to remove soluble by-products such as Na+, Cl−, and Al3+ remained in the zeolite. According to the above process, the molecular sieve is immobilized and fixed, and a gas of SiCl4 carried by a dried air is used, and the purge with air is conducted after the reaction. The process cannot be conducted in a continuous manner and has a low product capability.
CN1281493C discloses a rare-earth containing high silica Y-type zeolite and a process for preparing the same. The zeolite contains rare-earth, and has a Si/Al ratio of 5-30, an initial unit cell size of 2.430-2.465 nm, and a ratio of the balanced unit cell size to the initial unit cell size of at least 0.985. The process for preparing the zeolite comprises contacting the rare-earth containing Y-type zeolite with tetrachlorosilane. The contact can be conducted in a reaction apparatus, which is as shown in FIG. 1 and comprises a reaction vessel (1), an inlet (2) and a gas outlet (3). A stirrer (4) is provided inside the reaction vessel (1). A gas-solid separator (5) is installed at the gas outlet (3). The pore diameter and the porosity of the pores contained in the gas-solid separator (5) can ensure that the gas can pass through the pores, but the zeolite solid particles cannot. The stirring rod of the stirrer (4) extends beyond the reaction vessel (1). Under the stirring of the stirrer (4), the rare-earth containing Y-type zeolite is contacted with tetrachlorosilane at 100-500° C. for 5 minutes to 10 hours. The weight ratio of the rare-earth containing Y-type zeolite to tetrachlorosilane is 1:0.05-0.5. The rare-earth containing Y-type zeolite has a Si/Al ratio of 3 to 8 and a unit cell size of 2.45-2.48 nm. It is clear that this process generally requires a long contact time, for example, of several hours. Considering the time for charging before the reaction and discharging after the reaction, in average, the above dealumination and silicon insertion reaction can be conducted at the very most only once in a day shift and only twice even in a day/night shift. Moreover, since it requires the stirring in the reaction vessel, the size of reaction vessel cannot be too large. Under the current situation, the largest reaction vessel for the above dealumination and silicon insertion reaction has a production capability of 600 kg. The further increase in the size of the reaction vessel will result in an insufficient stirring. Therefore, with the above reaction vessel, 1200 kg of high silica molecular sieve can be obtained at the very most per day. Furthermore, in the above prior art process, in order to ensure the high silica content of the obtained molecular sieve, an excessive amount of SiCl4 is used. The use of the excessive amount of SiCl4 undoubtedly increases the production cost and the environment protection cost. On the other hand, the above process needs very multifarious manual operations, such as manual charging, manual discharging and a long time pipeline purge after the reaction. These operations not only bring a large manual labor intensity and have the problem of low production efficiency, but also bring a serious environment pollution and a serious hazard to the healthy of the operation works due to the molecular sieve dust formed during the charging and the discharging and the excessive SiCl4. Therefore, the above gas-phase ultra-stabilization with the reaction vessel is difficult for the industrial production.
CN102049315A discloses a process for preparing the catalyst. The process comprises the molecular sieve is flowed in an inert carrier gas flow with the entrainment of the inert carrier gas flow, and is contacted with the gaseous SiCl4 in a flowing condition. The contact time between the molecular sieve and the gaseous SiCl4 is 10 seconds to 100 minutes. Then the resulting molecular sieve that has been contacted with the gaseous SiCl4 is mixed with a binder, a clay and water into slurry and shaped into particles to produce the catalytic cracking catalyst. According to the above process, the preparation of the catalytic cracking catalyst can accomplish the continuous contact and reaction of the molecular sieve and SiCl4. By controlling the flow rate of the carrier gas and the length of the tube reactor, the contact time between the molecular sieve and SiCl4 can be controlled, and therefore the contact and reaction between the molecular sieve and SiCl4 in the tube reactor can be sufficient. However, according to the above process, the gas-phase ultra-stabilization reaction is conducted with a gas to carry the molecular sieve powder to contact and react with the SiCl4 gas. In order to fluidize the molecular sieve, a large amount of the gas should be used. The weight ratio of the carrier gas to SiCl4 can reach 10-250. Otherwise, it will be easy to block the apparatus. The increase of the gas amount can result in that it is difficult to increase the depth of the dealumination and silicon insertion reaction. There is an inherent conflict between the solid convey and the increase in the depth of the dealumination and silicon insertion reaction. In addition, according to the above process, in order to reach a certain reaction degree, a large amount of SiCl4 is needed. This will bring about the increase in the residual amount of SiCl4 after the gas-phase ultra-stabilization reaction, which not only exacerates the harmful environment pollution but also is unfavorable for the effective absorption of the tail gas.
CN102049315A and CN102452660A disclose the gas-phase processes for preparing the high silica molecular sieve. According to those processes, the molecular sieve and SiCl4 are contacted in the presence of inert carrier gas. The inert carrier gas can provide the kinetic energy for the molecular sieve solid powder to overcome the gravitational potential energy, so that the molecular sieve solid powder can be moved upward from the bottom of the reactor along with the gaseous SiCl4, during which, the molecular sieve and SiCl4 are contacted and reacted. CN102452660A discloses mixing the molecular sieve and a gas containing the gaseous SiCl4 to form a mixed stream (wherein the gas containing the gaseous SiCl4 can be the gaseous SiCl4). In the mixed stream, the molecular sieve flow along with the gas, and contacts the gaseous SiCl4 in the gas in a flowing state. Although CN102452660A hints that SiCl4 can be used as both the carrier gas and the reactant, however fails to make any detailed discussion in this aspect. Indeed, in the reaction, the molecular sieve is conveyed by the carrier gas from bottom to top, if only using SiCl4 as carrier gas without any other inert carrier gas, it needs a large amount of the SiCl4 gas. However, if using a large amount of SiCl4 to contact with the molecular sieve, the reaction temperature of the gas-phase ultra-stabilization reaction will result in a very severe gas-phase ultra-stabilization reaction, and must result in that the molecular sieve product after the gas-phase ultra-stabilization reaction has a large loss in the crystallinity. Usually, if the weight ratio of SiCl4 to the molecular sieve is higher than 1, at the beginning of the gas-phase ultra-stabilization reaction, the gas-phase ultra-stabilization reaction will be very severe. The molecular sieve product after the gas-phase ultra-stabilization reaction has a relative crystallinity of less than 40%, even less than 30%. This is unfavorable for retaining the relative crystallinity of the molecular sieve product. In addition, from the aspects of the absorption of the tail gas after the gas-phase ultra-stabilization reaction and the environment pollution, if using SiCl4 as carrier gas to convey the molecular sieve solid powder, the amount of SiCl4 is huge, and it is undoubtedly that a large amount of SiCl4 was left after the gas-phase ultra-stabilization reaction. The absorption of the tail gas will become very difficult, and the environmental pollution will become a severe problem too. Moreover, from the analysis about the economic cost, SiCl4 is costly, and using a large amount of SiCl4 as carrier gas is impermissible in economics. Therefore, using SiCl4 as carrier gas to convey the molecular sieve solid powder is infeasible. Therefore, it is impossible for the gas-phase ultra-stabilization reaction in CN102452660A to use SiCl4 as carrier gas to convey the molecular sieve solid powder.